A drive axle of a road or off-road vehicle typically has a differential gear mechanism which enables its right and left drive wheels to rotate at different speeds during certain conditions including steering of the vehicle along a turning radius and occurrence of a difference between traction of one drive wheel to an underlying surface and traction of the other drive wheel to an underlying surface. When a drive axle has a locking differential, it includes a locking/unlocking mechanism. When the locking/unlocking mechanism is unlocked, the differential gear mechanism operates as described. When the locking/unlocking mechanism is unlocked, the right and left axle shafts are locked together to cause the right and left drive wheels to rotate in unison and thereby disable their rotation at different speeds.
Current locking differential drive axles may be manually activated by a driver of a vehicle, and then either manually or automatically deactivated. When a driver wants to lock the differential, certain contemporaneous events such as wheel spin and steering angle of the vehicle render locking undesirable or even impossible.
For example, a driver may have to bring a vehicle to a near or complete stop in order to lock the differential, and such stopping may be hazardous in certain circumstances, such as when a vehicle is travelling on a high speed roadway or is operating off-road.
If the differential is already locked, and then prematurely unlocked, it can be re-locked only in the above manner.
Consequently, in intermittent low traction conditions, a driver must decide either to tolerate the stop/slow down engage/disengage cycle, to leave the differential unlocked and risk a low traction event, such as getting stuck or being forced to drive more slowly in order to maintain vehicle control, or to leave the differential locked for extended periods of time and risk increased tire wear and reduced driveshaft life due to equivalent left and right wheel speeds, during turning events, causing intermittent wheel slip and grip.
Two types of differential locking/unlocking systems are sometimes referred to as “mechanical coupler” and “clutch pack” (“limited-slip”). The mechanical coupler cannot be used in a wheel spin event, unless the vehicle is stopped or nearly stopped, and there has not yet been a remedy to prevent that. The clutch pack engages/disengages automatically at almost any speed, but if engaged while the vehicle is in a turn, it has a tendency to cause understeering on low friction road surfaces.